Art of dehydrating apples



United States Patent 3,018,559 ART OF DEHYDRATING APPLES William R. Dorsey, Orinda, and Robert E. Kalbaugh, Sebastopol, Calif., assignors to Vacu-Dry Company, Oakland, Calif, a corporation of California No Drawing. Filed Jan. 23, 1958, Ser. No. 710,603 7 Claims. (Cl. 34-28) This invention relates to improvements in the art of dehydrating apples, and more particularly to the art of continuously air drying apples from the fresh state.

It is an object of this invention to provide a process in which fresh apples may be continuously air dried from the fresh state to a moisture contentof from 16 to 24%.

It is another object of this invention to provide a process in which fresh apples may be continuously air dried from the fresh state to a low moisture content of about 2 /2%.

It is a further object of this invention to provide a process for so dehydrating apples without damage at a rate of production much higher than the best rate which has heretofore been obtainable.

It is an additional object of this invention to increase such production by providing a critical control over the relative humidity of the heated air used for performing the evaporation down to the evaporated apple stage.

The foregoing and other objects of this invention will become apparent upon an understanding of the following specification setting forth the best mode contemplated by the applican-ts for carrying out their invention when considered in the light of the claims concluding the specification.

In the practice of their improved methods, the applicants use a continuous belt type air drier which forms no part of this invetnion. The air drier preferably used comprises a series of horizontally disposed perforated metallic conveyor belts mounted in housing means and provided with means for heating air and for circulating it through the belts. The physical equipment necessary to practice the process of this invention is well known to those skilled in the art and for that reason is not incorporated in any accompanying drawings. The type of belt and means of air circulation contemplated by the inventors is illustrated, for example, in the R.W. Callaghan et al. Patent 2,541,859, issued February 13, 1951, for Dehydrating Apple.

The drier used includes a series of six belts, each having two drying sections and includes means for heating the air being circulated to a temperature up to 280 F. The several belts are herein referred to as stages I, II, III, IV, V and VI, and the several drying sections are herein referred to as sections 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12. The air is delivered downwardly through the load from top to bottom and thence through the belt in drying sections 1, 2, 3, 4, 5, 6, 8, and 12, and upwardly through the belt and thence through the load from bottom to top in sections 7, 9, and 11.

In the practice of the process of this invention, whole apples are cored, peeled and sliced in the usual manner. The proper slice thickness is between A of an inch and of an inch, with an optimum thickness of of an inch.

After the fresh apples have undergone preliminary slicing and sulfur treatment, the fresh sliced apples are loaded upon the belt at the first drying stage at a belt load of between 13 pounds per square foot and 17 pounds per square foot, with an optimum loading of pounds per square foot. The air at the. first stage is blown downwardly through the load at a velocity of 200 feet per minute and at a temperature of 225 F. Approximately 30% of the air passing through the bed of apples is recirculated so as to maintain a relative humid- 3,0l3,55 Patented Jan. 30, 1962 ice ity of between 1 /2 and 2 /2% relative, with an optimum of slightly above 2% relative. The belt travel is such that stage I comprising sections 1 and 2 of the drier is continued for /2 hour.

Stage I is followed by a turnover and the partially dehydrated apples are loaded upon a second belt but at a belt loading equivalent to approximately 30 pounds of apples per square foot on a fresh basis. The air flow is directed downwardly for the first 15 minutes of stage II (section 3) and downwardly for the last 15 minutes of stage II (section 4). As before, the humidity is maintained slightly above 2% relative, and this is again done by recirculating approximately 30% of the air flowing through the bed of apples.

At the end of stage II the apples are again turned over and are loaded upon a third belt. The belt loading is increased to 45 pounds to square foot on a fresh basis. During stage III (sections 5 and 6), the air flows from top to bottom. The drying temperature during stage III is continued at 25 F. As before, the humidiy is maintained slightly above 2% relative, and this is again done by recirculating approximately 30% of the air flowing through the bed of apples. If this stage of the operation is continued for 30 minutes, there will be produced evaporated apples having a moisture content of approximately 16 to 24% with an optimum of 19 to 20% in far less time and with far less spoilage than has been obtainable by prior procedures.

As soon as but not before the apples have lost the major portion of their moisture, heated air, as applied in the foregoing steps. can be passed from bottom to top without destructive effects upon the apples.

If low moisture apples are to be produced, at the end of stage III the apples are turned over and loaded upon a belt at stage IV. The belt load is continued at 45 pounds per square foot on a fresh basis and the temperature is maintained at approximately F. Air flow in stage IV (sections 7 and 8) is alternated between upward flow (section 7) and downward flow (section 8). Stage IV continues for between 30 and 45 minutes and is followed by a turnover.

After the turnover, the partially dehydrated apples are transferred to stage V and thereafter to stage VI of the drier at a belt load of 45 pounds per square foot on a fresh basis. The temperature continues at approximately 175 F. for a time of between 30 and 45 minutes. The air flow continues to be alternated between upward (sections 9 and 11) and downward (sections 10 and 12) flow.

The chart listed below collects in tabular form the proper operating conditions for practicing applicants invention in the form best contemplated by them.

Section Load- Temrera- Humidity, Air Time,

ing, lb. ture, F. percent Flow min.

15 225-280 1% to 2A Down... 15

15 225-280 1% to 2 Down 15 30 4 Down 15 45 Down... 15

45 Down- 15 45 Down. 15-20 45 Down. 15-20 45 Down 15-20 By following the foregoing procedures it is possible for the first time to produce satisfactory evaporated apples from the fresh state on a continuous basis. Hithertofore it has been thought that the continuous process was inapplicable to fresh apples insofar as the fresh apples had tended to become damaged in attempts to dry them continuously. Applicants have discovered that by critical control of humidity and by the downward direction of air flow in the early stages of the operation that continuous evaporation is possible. In this connection, the downward direction of air fiow in the early stages of the drying operation is essential until the major portion of the moisture has been removed, and the control of humidity within the range of 1 /2 to 2 /2% is critical. If the humidity is under 1 /2% the product becomes seriously damaged; if it is over 2 /2%, the productivity is so low as to be without commercial consequence.

The disclosed temperature of 225 F. used in the first six sections of operation, that is, during the first hour and one-half of drying time, is not critical. If the humid ity is controlled as disclosed in this specification, the applicants have found that temperatures of 240 F. with more rapid drying may be used. With certain apples temperatures as high as 280 F. have been used with success.

By the use of the instant procedures, it is also possible for the first time to continuously produce low moisture apples having a moisture content of approximately 2 /2% from the fresh apple. Hithertofore the continuous process was thought to be applicable only after evaporated apples had been obtained by conventional methods. This is shown, for example, in the Callaghan et al. Patent 2,541,859, referred to herein, wherein the starting product is the conventional evaporated apple air dried in either kiln or tunnel driers.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitation should be understood therefrom, for modifications will be obvious to those skilled in the art. Accordingly, the scope of the invention is defined in the appended claims.

We claim:

1. The method of dehydrating sliced fresh apple comprising forming said sliced fresh apple in a continuously moving layer; passing heated air downwardly through said moving layer of apples, maintaining the relative humidity of said air at approximately 2% relative humidity, and maintaining the temperature of said air not less than 225 F. and not more than 280 F. until the major portion of the moisture content has been evaporated; and thereafter passing heated air through said moving layer of apples until said apples have been reduced to a moisture content within the range of 16 to 24%.

2. The method of dehydrating fresh apple pieces comprising forming said fresh apple pieces in a continuously moving layer; passing heated air downwardly through said moving layer of apples, maintaining the relative humidity of said air within the limits of 1 /2 to 2 /2% relative humidity, and maintaining the temperature of said air not less than 225 F. and not more than 280 F. until the major portion of the moisture content has been evaporated; and thereafter passing heated air through said moving layer of apples until said apples 4 have been reduced to a moisture content within the range of 16 to 24%.

3. The method of dehydrating sliced fresh apple comprising forming said sliced fresh apple in a continuously moving layer; passing heated air downwardly through said moving layer of apples, maintaining the relative humidity of said air within the limits of 1 /2 to 2 /2% relative humidity, and maintaining the temperature of said air not less than 225 F. and not more than 280 F. until the major portion of the moisture content has been evaporated; and thereafter passing heater air through said moving layer of apples until said apples have been reduced to a low moisture content of approximately 2 /2%.

4. The method of dehydrating fresh apple pieces comprising forming said fresh apple pieces in a continuously moving layer; passing heated air downwardly through said moving layer of apples, maintaining the relative humidity of said air at approximately 2% relative humidity, and maintaining the temperature of said air not less than 225 F. and not more than 280 F. until the major portion of the moisture content has been evaporated; and thereafter passing air through said moving layer of apples until said apples have been reduced to a low moisture content of approximately 2 /z%.

5. In a method for dehydrating fresh apple pieces, the steps of forming said fresh apple pieces into a continuously moving layer; and of passing heated air having a relative humidity within the range of 1 /2 to 2/2% downwardly through said moving layer of apples until the major portion of the moisture content of said apples has been evaporated.

6. The method for dehydrating sliced fresh apple pieces including forming said sliced fresh apple pieces into a continuously moving layer; and passing heated air downwardly through said moving layer of apple pieces and maintaining the relative humidity of said air at not less than 1 /2% until the major portion of the moisture content of the said apple pieces has been evaporated.

7. In a method for dehydrating sliced fresh apple the References Cited in the file of this patent UNITED STATES PATENTS 2,155,453 Stuntz Apr. 25, 1939 2,541,859 Callaghan et al. Feb. 15, 1951 2,799,096 Scott July 16, 1957 2,895,836 Lazar et al. July 21, 1959 

6. THE METHOD FOR DEHYDRATING SLICED FRESH APPLE PIECES INCLUDING FORMING SAID SLICED FRESH APPLE PIECES INTO A CONTINUOUSLY MAVING LAYER; AND PASSING HEATED AIR DOWNWARDLY THROUGH SAID MOVING LAYER OF APPLE PIECES AND MAINTAINING THE RELATIVE HUMIDITY OF SAID AIR AT NOT LESS THAN 1 1/2% UNTIL THE MAJOR PORTION OF THE MOISTURE CONTENT OF THE SAID APPLE PIECES HAS BEEN EVAPORATED. 